Mechanical properties of heart muscle determine to a great extent the way in which biochemical events in the cell are transduced into muscle tension and ultimately into development of pressure in the heart. Changes in the mechanical properties of the aged heart could account for the observed changes in cardiac performance as determined by a variety of indices. This program uses vibration techniques to measure the components of a cardiac and vascular muscle which determine the overall "stiffness", and measures the age induced effects on stiffness produced by regulatory events of both neurohumoral and mechanical origins. As the major elements of cardiac control, these events, and their interaction with the mechanical properties of the heart, form the basis for cardiac control. BIBLIOGRAPHIC REFERENCE: Spurgeon, J.A., Thorne, P.R., Yin, F.C.P., Shock, N.W., and Weisfeldt, M.L.: Increased dynamic stiffness of trabeculae carneae from senescent rats. Am. J. Physiol. 232: H373-H380, 1977.